1. Technical Field
The present invention relates to a disposable absorbent article having a body-facing adhesive to be positioned against a wearer""s skin. In one aspect, the invention relates to a catamenial device having a supportive adhesive residing on the body-side surface of the device.
2. Background
Externally positioned, disposable absorbent articles in the form of a catamenial device, configured for the absorption of body fluids such as menses, collectively are referred to herein as a sanitary napkin.
The sanitary napkin is secured during use, often by attaching the sanitary napkin to the wearer""s undergarment by an adhesive.
When a sanitary napkin is secured to an undergarment, the wearer may experience a number of drawbacks or disadvantages. One drawback is that the adhesive can stick too aggressively to the inside surface of the undergarment leaving a residue. Another disadvantage is the napkin will tend to move with the undergarment rather than associating with the bodily movements of the wearer. This undesirable movement can result in a less secure fit and can increase the incidence of fluid leakage, irritation, chafing, and discomfort.
Attempts made to adhere a sanitary napkin directly to the wearer require an adhesive compatible with the wearer""s skin. In securing the sanitary napkin directly to the wearer, adhesives of the type used in various surgical applications could be employed. However, removal of these adhesives causes sudden pain and discomfort to the wearer in the sensitive pudendal region.
Thus, sanitary napkins could be employed large enough to avoid applying such adhesive in contact with the wearer""s pubic hair and sensitive genitalia. However, such large sanitary napkins are found to be uncomfortable to the wearer, and they are noticeable through the wearer""s outer garments.
A sanitary napkin is needed which would be secured directly to the wearer""s body, which would be comfortable to wear, which would be discrete in appearance as viewed through the wearer""s outer garments, which would give the wearer a feeling of security during use, which would not cause discomfort upon removal from the wearer""s skin and hair, and which would not cause discomfort upon removal from the wearer""s skin and hair in the sensitive pudendal region.
Very few adhesive compositions are completely satisfactory for application to human skin. The requirements for such adhesives are stringent. They must adhere well to human skin during perspiration, when the weather is hot, or in an environment of draining wounds, yet be removable without leaving adhesive residue on the skin""s surface. Adhesion should take effect immediately on application to skin, even in a hot or moist environment, and should release cleanly and with minimal discomfort when voluntarily removed in this environment.
Adhesives applied to sensitive areas of the human body require further special characteristics. Hair covered regions are especially difficult to adhere to well without causing pain upon removal of the adhered article. For such regions, a soft adhesive with specific viscoelastic properties is required. Hydrogels could be used effectively for such purposes, but hydrogels have their own disadvantages, including high price, special packaging and release layers to retain the moisture (typically about 40% of the total adhesive), as well as variations in properties during use in response to changes in humidity. Other disadvantages arise from the general necessity of a non-woven support to strengthen the adhesive and hold it in place during cure. When cured, a water impervious release layer is applied.
To obtain a soft adhesive while maintaining solid-like behavior requires high molecular weight polymers. With hydrogels, this is obtained by cross linking or curing after cooling, as is the case with an electron beam curable acrylic described in European Patent Application EP 175562 A2. Further, U.S. Pat. No. 5,262,468 to Chen describes the use of very high molecular weight rubbers to obtain gelatinous thermoplastic compositions, but such compositions generally lack in adhesive grab so that virtually no adhesion to the body is obtained.
It is an object of the present invention to provide an absorbent article which is adhesively attached directly to the wearer""s body.
It is an object of the present invention to provide an absorbent article which is adhesively attached directly to the wearer""s body and which is small enough to be discrete and not noticeable through the wearer""s outer garments.
It is an object of the present invention to provide an absorbent article which is adhesively attached directly to the wearer""s body in the sensitive pudendal area.
It is another object of the present invention to provide a sanitary napkin which uses an adhesive having specific rheological properties to secure the sanitary napkin directly to the wearer in the sensitive pudendal area.
It is yet another object of the present invention to provide a sanitary napkin which is comfortable to wear and can be readily removed with little or no pain or discomfort to the wearer in the sensitive pudendal area.
It is yet another object of the present invention to provide a sanitary napkin with the desirable characteristics of a hydrogel adhesive, but without the drawbacks or disadvantages.
Other objects and advantages of the present invention will become apparent from the detailed description and accompanying drawings which follow.
The article of the present invention includes a sanitary napkin having an absorbent core with at least one body-facing surface designed to be positioned against the wearer""s body and a pressure sensitive adhesive secured to the body-facing surface. In one aspect, the article is limited in dimension and includes a hot melt adhesive to be pressed against the wearer""s pudendal region and characterized by a midblock Tg of less than xe2x88x9210xc2x0 C., a Gxe2x80x2 (storage modulus) less than 15xc3x97104 dynes/cm2 at 10 rad/s. (25xc2x0 C.), a Gxe2x80x3 (loss modulus) of 1 to 6xc3x97104 dynes/cm2, a tensile strength greater than 10 psi, and requiring no subsequent curing operation after cooling. In one aspect, the article includes an adhesive to be pressed against the wearer""s pudendal region which has an adhesive weight less than 1500 mg per square inch and a tan delta residing inside a quadrangle ABCD wherein said quadrangle ABCD is defined by graphically plotting frequency in radians per second versus tan delta referenced to about 20xc2x0 Centigrade of the adhesive, the quadrangle ABCD having as points A and D a tan delta of about 0.01 and about 0.6 respectively at a frequency of about 0.1 radians per second and points B and C at a tan delta of about 0.1 and about 1.7 respectively at a frequency of about 1000 radians per second.